PLANT SECONDARY METABOLITE DIVERSITY AS A RESISTANCE TRAIT AGAINST INSECTS - A TEST WITH SITOPHILUS-GRANARIUS (COLEOPTERA, CURCULIONIDAE) AND SEED SECONDARY METABOLITES
I. Castellanos et Fj. Espinosagarcia, PLANT SECONDARY METABOLITE DIVERSITY AS A RESISTANCE TRAIT AGAINST INSECTS - A TEST WITH SITOPHILUS-GRANARIUS (COLEOPTERA, CURCULIONIDAE) AND SEED SECONDARY METABOLITES, Biochemical systematics and ecology, 25(7), 1997, pp. 591-602
A hypothesis is tested about the functioning of plant secondary metabo
lite diversity taking into account the role of concentration of mixtur
es or single compounds: a high diversity secondary metabolite mixture
in high concentration provides a more effective protection against her
bivores than single compounds or low diversity mixtures in both low an
d high concentrations. Additionally the role of two unusual secondary
metabolites for a weevil when they are incorporated in its diet is exp
lored. Number of eggs laid and diet consumption are measured in the gr
anary weevil Sitophilus granarius exposed to cereal and non-cereal sec
ondary metabolites incorporated in artificial diets to test the hypoth
esis. Artificial diets had one, two, four or six compounds. The mixtur
es or single compounds were offered simultaneously to the weevils in c
oncentrations ranging from 0.05 to 5mgg(-1) in a multiple choice exper
iment. Low oviposition in high concentration six compounds mixture sup
ported the hypothesis. However, low oviposition in a low concentration
mixture of four compounds suggests that a moderate diversity may be e
qually functional in low and high concentrations. Diet consumption by
the weevil was not affected by concentration but an increasing number
of compounds in the diet reduced it slightly but significantly. The un
usual secondary metabolites for the weevil were less or equally effect
ive reducing oviposition and consumption as usual compounds did. (C) 1
997 Elsevier Science Ltd.